Electronic circuit systems are typically made by defining complex integrated circuit structures on semiconductor chips, bonding the chips to circuit package substrates, and in turn bonding the packages to printed circuit boards. The most common bonding technique is wire bonding, in which an instrument (a thermode) thermocompression bonds wire to a bonding pad of one element, such as a chip, and then pulls the wire and makes a bond on a bonding pad of a second element so as to form an arcuate self-supporting wire bridge between the two bonding pads.
An alternative to wire bonding which has found a substantial degree of commercial acceptance is tape automated (TAB) bonding, a technique described, for example, in the publication "The Basics of Tape Automated Bonding," Hybrid Circuit Technology, November 1984, Pages 15-21. In TAB bonding, a dielectric tape contains conductors to be bonded to a chip. The conductors overlap in cantilever fashion a window in the tape such as to match a row of bonding pads arranged on the periphery of the chip. Solder bumps on the ends of the conductors may be bonded by reflow soldering to the bonding pads of the chip. A dielectric tape may contain a large number of such windows which permits automated soldering of conductor arrays to successive chips. Opposite ends of the conductors may thereafter be bonded, for example, to a package substrate.
A trend that has been clear for a number of years in the integrated circuit field has been a steady increase in the density of conductors used on semiconductors chips, package substrates, and printed circuit boards. The bonding pads that must be used for making an interconnection between each conductor of one element and the circuitry of another element must typically be wider than the width of the conductors to accommodate the bonding process. Thus, there has been difficulty in arranging on the periphery of a chip, for example, all of the bonding pads needed for accommodating all of the conductors of the chip. If care is not taken in the proper organization of bonding pads, one obviously runs the risk of accidental short circuits. For example, in wire bonding, the wire interconnection may sag if designed to bridge too great a distance. TAB bonding assumes the organization of bonding pads in a peripheral array, which is inherently limiting.